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Spintronics

Spintronics

The goal of spintronic devices is to exploit the spin as well as the charge of the electrons that pass through them - using a spin current.

In a lateral spin transistor (Datta & Das, Appl. Phys. Lett., 1990) spin-polarised electrons are injected from a ferromagnetic source into a narrow semiconductor channel in which the electron spins can only move in the confined plane or wire. Here, the spin can be switched between up and down by an applied magnetic field, and eventually by the gate voltage, which thus determines the output spin current in the ferromagnetic drain material. Spin precession motion will be controlled by the external electric field, which imposes onto the trajectory and the state of moving electron spins due to spin-orbit interaction. This will result in altering the output voltage and make the spin device work with a spin degree of freedom. In the group, we are pursuing to understand the physics behind and provide a prototype of this spin device with well-established facilities.

spintronics1

The prerequisite of spin devices mentioned above is to inject spin-polarised current into non-magnetic materials, i.e. semiconductors. There has no efficient spin injection techniques so far and therefore the understanding of underlying physics on spin dependent transport is highly demanded. In our group, we are using circularly polarised photons as a source of spin polarised current in GaAs via the selection rules during photoexcitation1. The photoexcited carriers are transported towards a ferromagnetic metal/semiconductor interface by applied bias voltage and the efficiency of spin filtering can be investigated (Fig. 2).

spintronics2

Reference:


[1] J. A. C. Bland, S. J. Steinmuller, A. Hirohata, and T. Taniyama, Optical Studies of Electron Spin Transmission, in J. A. C. Bland and B. Heinrich, editors, Ultrathin Magnetic Structures IV: Applications of Nanomagnetism, Springer Verlag, Berlin (2005)

[2] S. J. Steinmuller et al., Phys. Rev. B, 72, 045301, (2005), Speration of electron spin filtering and magnetic circular dichroism effects in photoexcitation studies of hybrid ferromagnet/GaAs Schottky barrier structures.

[3] H. Kurebayashi et al., Appl. Phys. Lett., 91, 102114, (2007), Initial/final state selection of the spin polarisation in electron tunnelling across an epitaxial Fe/GaAs (001) interface.

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